The airway epithelium is known to play an integral role in the airway defense mechanism via the mucociliary system and mechanical barriers. Recent studies indicate that airway epithelial cells (AEC) can be activated to produce and release biological mediators important in the pathogenesis of multiple airway disorders (Polito and Proud, 1998; Takizawa, 1998). Evidence has shown that the epithelium is fundamentally disordered in chronic airway disorders such as asthma, chronic bronchitis, emphysema, and cystic fibrosis (Holgate et al., 1999; Jeffery P K, 1991; Salvato, 1968; Glynn and Michaels, 1960). One of the hallmarks of these airway disorders is the over-production of mucus by AEC. The major macromolecular components of mucus are the large glycoproteins known as mucins. Recently, the molecular structure of at least 7 human mucins was determined. The known mucin transcripts are heterogeneous with no sequence homology between the genes (Voynow and Rose, 1994), yet they are similar in their overall repetitive structure.
Deleterious stimuli are known to activate AEC. These stimuli can vary from antigens in allergic disease to drugs or environmental pollutants, tobacco smoke, and infectious agents associated with forms of chronic obstructive pulmonary disease. AEC activation leads to altered ion transport, changes in ciliary beating, and the increased production and secretion of mucins leading to increased mucus. The mediators produced in response to AEC activation include chemokines that promote the influx of inflammatory cells (Takizawa, 1998). These inflammatory cells can in turn produce mediators that may injure AEC. AEC injury stimulates cellular proliferation (goblet cell and submucosal gland cell hyperplasia) that results in an expanded and continuous source of pro-inflammatory products, including proteases as well as growth factors that drive airway wall remodeling that can lead to lung destruction and the loss of function (Holgate et al., 1999).
The over-production of mucus and alteration of its physiochemical characteristics can contribute to lung pathology in a number of ways. Disruption of physiologic mucociliary clearance by the over-production of mucins can lead to mucus plugging, air trapping, and atelectasis which is often complicated by infection.
Asthma is a chronic obstructive lung disorder that appears to be increasing in prevalence and severity (Gergen and Weiss, 1992). It is estimated that 30-40% of the population suffers with atopic allergy and 15% of children and 5% of adults in the population suffer from asthma (Gergen and Weiss, 1992).
In asthma, activation of the immune system by antigens leads to allergic inflammation. When this type of immune activation occurs it is accompanied by pulmonary inflammation, bronchial hyperresponsiveness, goblet cell and submucosal gland hyperplasia, and mucin over-production and hyper-secretion (Basle et al., 1989) (Paillasse, 1989) (Bosque et al., 1990). Mucus over-production and plugging associated with goblet cell and submucosal gland cell hyperplasia is an important part of the pathology of asthma and has been described on examination of the airways of both mild asthmatics and individuals who have died with status asthmaticus (Earle, 1953) (Cardell and Pearson, 1959) (Dunnill, 1960) (Dunnill et al., 1969) (Aikawa et al., 1992) (Cutz et al., 1978). Certain inflammatory cells are important in this reaction including T cells, antigen presenting cells, B cells that produce IgE, basophils that bind IgE, and eosinophils. These inflammatory cells accumulate at the site of allergic inflammation and the toxic products they release contribute to the destruction of AEC and other tissues related to these disorders.
In the related patent applications mentioned above, applicants have demonstrated that interleukin-9 (IL9), its receptor and activities effected by IL9 are the appropriate targets for therapeutic intervention in atopic allergy, asthma and related disorders. Mediator release from mast cells by allergen has long been considered a critical initiating event in allergy. IL9 was originally identified as a mast cell growth factor and it has been demonstrated that IL9 up-regulates the expression of mast cell proteases including MCP-1, MCP-2, MCP-4 (Eklund et al., 1993) and granzyme B (Louahed et al, 1995). Thus, IL9 appears to serve a role in the proliferation and differentiation of mast cells. Moreover, IL9 up-regulates the expression of the alpha chain of the high affinity IgE receptor (Dugas et al., 1993). Furthermore, both in vitro and in vivo studies have shown IL9 to potentiate the release of IgE from primed B cells (Petit-Frere et al, 1993).
Recently, IL9 was shown to stimulate mucin synthesis and may account for as much as 50-60% of the mucin-stimulating activity of lung fluids in allergic airway disease (Longpre et al., 1999). A gross up-regulation of mucin synthesis and mucus over-production occurs in IL9 transgenic mice as compared to mice from the background strain. IL9 specifically up-regulates the MUC2 and MUC5AC genes and proteins in vitro and in vivo (Louahed et al., 2000). Moreover, IL9 neutralizing antibody inhibits completely the up-regulation of mucins in response to antigen challenge in animal models of asthma (McLane et al, 2000).
Current asthma treatments suffer from a number of disadvantages. The main therapeutic agents, beta-receptor agonists, reduce the symptoms thereby transiently improving pulmonary function, but do not affect the underlying inflammation nor do they suppress mucin production. In addition, constant use of beta-receptor agonists results in desensitization, which reduces their efficacy and safety (Molinoff et al., 1995). The agents that can diminish the underlying inflammation, and thereby decrease mucin production, such as anti-inflammatory steroids, have their own list of disadvantages that range from immunosuppression to bone loss (Molinoff et al., 1995).
Chronic bronchitis is another form of chronic obstructive pulmonary disorder. Nearly 5% of adults suffer with this pulmonary disorder. Chronic bronchitis is defined as the chronic over-production of sputum. Mucus over-production is generally associated with inflammation of the conducting airways. The mediators of inflammatory cells including neutrophils and macrophages may be associated with increased mucin gene expression in this disorder (Voynow et al., 1999; Borchers et al., 1999). The increased production of mucus is associated with airway obstruction, which is one of the cardinal features of this pulmonary disorder. Therapy is largely symptomatic and focused on controlling infection and preventing further loss of lung function. Decongestants, expectorants and combinations of these agents that are often used to treat the symptoms of bronchitis are not thought to alter mucin production. Mucolytics may promote mucociliary clearance and provide symptomatic relief by reducing the viscosity and/or the elasticity of the airway secretions but do not inhibit mucin synthesis or mucus over-production. (Takahashi et al., 1998
Cystic fibrosis (CF) is yet another disease that effects the lung and is associated with thick secretions resulting in airway obstruction and subsequent colonization and infection by inhaled pathogenic microorganisms (Eng et al, 1996. DNA levels are increased significantly in CF lung and can increase the viscosity of sputum. While recombinant aerosolized DNAse is of value these patients, there is no effective treatment for the pathologic mucus over-production. Thus, there is a specific unmet need in the art for the identification of agents capable of inhibiting mucin over-production by airway epithelial cells in CF. In addition to the airway obstruction caused by mucin secretions, CF patients also suffer from mucus plugging in the pancreatic ducts which prevent the delivery of digestive enzymes to the GI tract. The result is malabsorption syndrome, steatorrhea and diarrhea.
While mucus over-production is one of the hallmarks of multiple chronic obstructive lung disorders, the art lacks any methods to block the synthesis or over-production of mucins associated with these pulmonary disorders. Thus, there is a specific need in the art to inhibit the over-production of mucins and thin the secretions of these patients to promote mucociliary clearance and preserve lung function.